The influence of direct microwave irradiation (2.45 GHz, CW) of the intact exposed heart on cardiac function in cats with and without myocardial ischemia is being examined. Myocardial ischemia (MI) is induced by occlusion of the left anterior descending coronary artery. In the sham and sham-plus-microwave exposed animals the coronary artery is isolated but not occluded. The exposed hearts are irradiated at a specific absorption rate of 30 mW/g or sham irradiated and are monitored for 5 hours. Mean arterial blood pressure (MABP), cardiac output (CO), heart rate (HR), plasma and myocardial creatine phosphokinase (CPK), and S-T segment are not influenced by microwave irradiation of the myocardium. Furthermore, in the MI-plus-microwaves and MI cats, comparable values of MABP (124 vs 114 mmHg), (128 vs 130 ml/min kg), HR (119 vs 124 beats/min), plasma CPK (8.5 vs 9.0 IU/mg protein) and S-T segment (0.60 vs 0.63 mV) are observed at 5 hr post occlusion. Thus, the results suggest that 5-hour exposure of the cat myocardium to microwave radiation has no effect on the parameters examined. In addition, this environmental factor has no influence on the course of the acute myocardial ischemia in cats.